*3.2. Representativeness of the Translational Machinery and RNA Binding Proteins in the L. infantum Experimental Proteome*

Around 200 proteins from the *L. infantum* promastigote proteome were categorized as components of the translational machinery: 122 ribosomal proteins, 51 translation regulatory factors, and 24 tRNA synthases (Supplementary File, Table S2). As expected for a highly proliferative stage (the promastigotes were growing in the logarithmic phase when harvested for analysis), in which protein synthesis needs to be very active, all the ribosome components, tRNA-loading enzymes, and regulatory factors were abundant and easily detected by mass spectrometry. Nevertheless, in contrast, very few of the annotated mitoribosomal proteins [39] were identified in the *L. infantum* promastigote proteome. This observation may indicate that mitochondrial ribosomes are in relatively low amounts when promastigotes are grown in nutrient-rich culture media.

Proteins with RNA binding properties deserve special attention, since gene expression in *Leishmania* and related trypanosomatids is essentially being controlled at the post-transcriptional level [40,41]. In this scenario, RNA-binding proteins are key players in controlling RNA metabolism [42–44]. In the *L. infantum* promastigote proteome, a large number of known RNA binding proteins were detected (Supplementary File, Table S3). Apart from the mentioned ribosomal proteins and translation factors, 15 RNA helicases were detected, as well as many of the RNA-binding domain-containing proteins reported in a recent study aimed to the capture and identification of RNA-bound proteins in *L. donovani* [45]. The RNA-binding proteins of the Pumilio family (aka PUF proteins) are especially numerous (11 members) in *Leishmania* [46]. In this study, we identified 6 out of 11 PUF proteins that are being expressed in the promastigote stage of *L. infantum*; these are PUF 1, PUF 4, PUF 6, PUF 7, PUF 8, and PUF 10 (see Table S3 to see their gene IDs).
